This invention relates to mowing vehicles in general and particularly to such vehicles that are responsive to changes in terrain, such that the vehicle body is maintained in a generally vertical orientation.
Mowing vehicles, such as riding lawnmowers and tractors with mowing attachments, have long been used in mowing hillsides, particularly by highway maintenance personnel. Most of these vehicles do not provide means for adapting to changing terrain, such that when a vehicle is on a slope the frame tilts accordingly, which can result in the vehicle tipping over. Prior attempts to remedy this problem have included adapting existing mowing machines by providing mechanical actuation of a mower blade assembly to conform to the slope without significantly modifying the vehicle frame itself. Such modified mowers are limited in the degree of and types of slopes upon which they can be effectively and safely operated. Other devices have involved three- or four-wheeled vehicle frames with complex actuation of fixed deck blade housings.
These prior art devices have proven to be only somewhat effective in mowing slopes and have been very expensive, prohibiting many small operators and municipalities from using them.
U.S. Pat. No. 4,707,971 for a SLOPE MOWER and U.S. Pat. No. 4,869,054 for a SLOPE MOWER WITH SIDE FRAMES are directed to a mower designed to remain upright during use on a hill so the mower does not tip over and are incorporated herein by reference. These patents, assigned to the assignee of the present application, are directed to slope mowers which attempt to remedy the above problems. These mowers include a vehicle frame with single front and rear driven wheels. The vehicle frame is maintained in a generally upright or vertically aligned orientation by side-mounted hydraulic cylinder and piston rod arrangements which are actuated in response to a leveling system mounted on the vehicle frame. The leveling system senses changes in the attitude of the vehicle frame and selectively actuates the hydraulic cylinder arrangements to maintain the vehicle frame in an upright position. In U.S. Pat. No. 4,707,971, the hydraulic cylinder and piston rods are attached to mower blade housings with ground engaging caster wheels on either side of the vehicle frame, which housings are pivotally connected to each other along the center longitudinal axis of the vehicle frame. In U.S. Pat. No. 4,869,054, the hydraulic cylinder and piston rod arrangements are connected to a pair of side frames with ground engaging outrigger wheels which are hinged to the vehicle frame. A pair of mower housings are floatably mounted beneath the respective side frames and hinged to the vehicle frame and to each other.
While the above noted mower embodiments were a major improvement over the prior art and have been generally satisfactory in mowing slopes up to 30 degrees while maintaining the vehicle frame and rider in a generally upright position, a number of drawbacks remain. In both patents, the pair of mower deck housings are hinged to each other via a piano type hinge underneath the vehicle frame, which means that the hinge must be located such that the pivot point connecting the blade housings is considerably higher than a plane containing the mower blades. This means that, particularly when the mower is being operated on terrain which slopes away from the vehicle frame on either side, the mower blades will not be parallel to the surface of the terrain, resulting in uneven cutting. Furthermore, both patents teach the use of mower housings which are mounted side-by-side with synchronized blades of overlapping arcs. This requires a relatively complex synchronized mechanical drive linkage to drive the separate mower blades. Lastly, in the case of U.S. Pat. No. 4,869,054, the side frames are hinged to the vehicle frame at a forward location, which arrangement requires the floating mower decks to be equipped with supporting and/or adjusting caster wheels at both the front and the rear of each mower housing.
Thus, it is clear that a need exists for a slope mower which evenly mows terrain even when it slopes away from the vehicle frame on either side. Such a mower should have excellent traction on slopes up to 30 degrees and should be relatively inexpensive to own and operate.